Such air heaters are common and are used extensively in industry. Used in many kinds of manufacturing processes, the air heaters heat the air that is supplied either by an external air source (blower) or by a blower that is attached directly to the air heater. The air is passed through a connecting case for the power supply, or it bypasses this case, and is then heated by a heating element.
Such air heaters must be of robust design to handle the generated heat as well as continuous operation. In addition, they should be designed for simple and quick assembly since a great number of such devices are produced in the course of mass production. In the air heater designs known so far, attaching the electrical connections in particular is a significant time-consuming factor during assembly.
From U.S. Pat. No. 5,033,208, a dry-air drying system for drying plastic granulates for plastic injection molding is known. A cylindrical housing contains two double-wall hollow cylinders of different diameters that are coaxial to each other and to the housing of the drying system. Between them, they form a drying chamber for the material to be dried. The walls of the hollow cylinders facing the drying chamber have openings serving as passages for heated air. The innermost hollow cylinder contains an electric heating system that heats the dry air supplied by a blower flanged to the outside of the housing before it enters the drying chamber. The heated air flows through the material to be dried in the drying chamber before entering the outer hollow cylinder from which it is purged by an exhaust air system.
It is common practice to make the electrical connections—especially with regard to their insulation from the housing—by means of flexible individual leads or flexible connection board connectors, where the electrical connection at the contact points is usually made with impulse welding or manual soldering. Making connections in this manner is time-consuming and leads to high assembly costs. In addition, there is a danger that the connection is interrupted by mechanical impacts or vibrations that would render the device inoperable. Another disadvantage of such connections made with leads is their labor-intensive disconnection in case of repairs.
In special applications, electrical connections are made with rubber-elastic electrically conductive connecting elements that do not have the disadvantages described above. Numerous designs of such elastic connecting elements for the electrical connection of components are known, and are being offered as ‘conductive rubber element’ by many manufacturers. The term ‘conductive rubber element’ indicates that it is a component with rubber-like characteristics that is electrically conductive, although it may not necessarily be made of rubber. The electrical conductivity of conductive rubber is achieved by adding conductive materials to the insulating base material. Such contact devices have long been used for the electrical connection of LCD displays with the conductors of connector circuit boards (DE 88 08 947 U1).
Difficulties with the use of conductive rubber elements occur whenever the components to be electrically connected are not parallel and/or if their surfaces are not flat. In such cases, specially shaped conductive rubber elements matching the geometry and the spatial orientation of the contact points to be connected are used. However, since such conductive rubber elements also need to have elastic properties, positive positioning, and thus the establishment of precise contact, is problematic because the conductive rubber elements may deform uncontrollably when the necessary contact pressure is generated.